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Many people at high risk of flu infection mistakenly believe they're in a low-risk group and, as a result, are much less likely to get a flu shot, a researcher from the University of North Carolina at Chapel Hill School of Public Health has found.

The study, conducted during the flu vaccine shortage of 2004-2005, found that underestimating risk was common, particularly among people less than 65 years old, said Dr. Noel T. Brewer, UNC assistant professor of health behavior and health education. Only 26 percent of younger adults at high risk were vaccinated that flu season, despite recommendations from the Centers for Disease Control and Prevention (CDC) urging high-risk groups to get a flu shot.

The results also indicate what messages will resonate with people and encourage those most likely to get the flu to be vaccinated, Brewer said. "We need to be clearer about who is in the high risk groups. If we can frame health messages around easily identifiable risk categories, then others - including family and friends of high risk individuals - can help persuade those at high risk to get their flu shot. This simple message could very well save lives."

Brewer notes that the vaccine shortage apparently discouraged some high-risk people from being vaccinated -- about 24 percent -- but the majority of study participants - 73 percent - said the shortage did not affect their behavior.

The study, lead by Brewer and Dr. William K. Hallman, professor of human ecology at Rutgers University, surveyed a random sample of 300 adults in September 2004 and March 2005. The researchers examined the number of people at high risk of getting the virus, as defined by the CDC, and assessed how many got vaccinations. High risk groups include older adults (age 65 or older) and people from 18 to 64 years old who had chronic health conditions. A third high priority group comprised people who had regular contact with high-risk adults or children. Reasons for not getting vaccinated were also examined.

Of the 300 people surveyed, half who met the CDC's criteria for being top priority for vaccination said they believed their risk was low, and as a result they were not vaccinated.

Also, though more than 60 percent of elderly adults were vaccinated, Brewer said, only 26 percent of younger adults at high risk and 36 percent of people who had regular contact with either of the other two groups were vaccinated.

"Underestimating one's risk was common, particularly among people under age 65," Brewer said. "Most older people understood their high risk, but two thirds of respondents in the other high risk categories mistakenly thought they were at low risk. Only a couple people overestimated their risk of infection."

The study also examined whether the news of a vaccine shortage during that flu season changed behaviors -- either prodding more people to seek vaccination or fewer. About a quarter (24 percent) said the shortage discouraged them from being vaccinated, while only three percent said the shortage encouraged them to get a flu shot. The vast majority, though (73 percent), said the shortage had no effect on their behavior.

"This study helps us understand what messages will resonate with people, and encourage those most likely to get the flu to be vaccinated," Brewer said. About 36,000 people in the United States die each year from flu-related illnesses, so vaccinating the people who would be in the most danger if they got sick is a critical public health priority, he said.